JP6179079B2 - Exhaust system - Google Patents

Description

  The present invention relates to an exhaust system in which gas heated by a burner device is mixed with exhaust gas flowing through an exhaust passage to assist oxidation of an oxidation catalyst.

  In some cases, fuel is further burned in the exhaust gas from the engine. For example, the regeneration process of the particulate filter which removes particulate matter (PM: Particulate Matter), such as soot, contained in exhaust gas in a diesel engine corresponds to it (for example, patent document 1).

  In such regeneration treatment, the temperature of the exhaust gas is raised by the oxidation catalyst. In order to quickly raise such an oxidation catalyst to the activation temperature, air is heated by a separate heater and introduced into the exhaust gas (for example, Patent Document 2), or fuel is injected into the exhaust passage (for example, Patent Documents 3 and 4) are known.

JP-A-5-222913 JP 2005-320880 A JP 2007-154772 A JP-A-8-260944

  As a heat source that assists in raising the temperature of the oxidation catalyst, there is a burner device that raises the temperature of the gas mixed with the exhaust gas, in addition to the heater and the fuel injection mechanism described above. In any case, the temperature of a part of the exhaust gas is raised, or a separately heated gas is mixed with the exhaust gas, so the temperature distribution is uneven and non-uniform in the flow path cross section.

  At this time, it is conceivable to provide a swirler, a baffle plate or the like downstream of the heat source to make the temperature distribution uniform, but the structure is complicated, leading to increased pressure loss and manufacturing cost.

  In view of such problems, an object of the present invention is to provide an exhaust system that can easily achieve uniform temperature distribution with a low-cost and simple configuration with low pressure loss.

In order to solve the above problems, an exhaust system of the present invention is provided with a particulate filter that collects particulate matter contained in exhaust gas exhausted from an engine, and upstream of the particulate filter, via a catalyst. An oxidation catalyst that raises the temperature of the exhaust gas by an oxidation reaction and an upstream of the oxidation catalyst, a part of the exhaust gas is allowed to flow into the exhaust gas so that the oxidation catalyst reaches the oxidation activation temperature, A burner device that is introduced perpendicularly to the flow of exhaust gas, and provided downstream of the burner device and upstream of the oxidation catalyst, the flow passage cross-sectional area is enlarged along the flow of exhaust gas, reduced, and a stirring portion formed of a rectangular parallelepiped, drained exhaust gas from the surface at the position of the surface perpendicular to flow into the exhaust gas relationship stirring portion formed in a rectangular parallelepiped, from the stirring unit Outflow direction of the exhaust gas leaving is characterized by the inflow direction and vertical exhaust gas flowing into the stirring section.

  According to the present invention, the mixing effect can be enhanced and the temperature distribution can be easily uniformed with a low-cost and simple configuration (stirring section) with low pressure loss.

It is explanatory drawing for demonstrating the exhaust system of a diesel engine. It is explanatory drawing for demonstrating the structure of a burner apparatus. It is explanatory drawing which compared the required air quantity at the time of idling of an engine. It is a cross-sectional view for demonstrating the structure of a stirring part. It is a cross-sectional view for explaining another structure of the stirring unit. It is a cross-sectional view for explaining still another structure of the stirring unit.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiments are merely examples for facilitating the understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present invention are not illustrated. To do.

(Exhaust system)
FIG. 1 is an explanatory diagram for explaining an exhaust system of the diesel engine 1. As shown in FIG. 1A, the diesel engine 1 is a reciprocating engine. Specifically, the air in the cylinder is compressed by a piston to increase the temperature and pressure, and the light oil and heavy oil stored in the fuel tank 2 are stored. The fuel pump 3 or the injection pump 4 is pressurized and injected into the high-temperature and high-pressure air to cause an explosion, and the energy generated by the explosion is converted into power. The supercharger 5 is a device that improves the engine output by rotating the turbine with the energy of the exhaust gas of the diesel engine 1 and compressing the intake air to increase the intake pressure.

  The exhaust passage 6 is constituted by piping for exhausting the exhaust gas discharged from the exhaust port of the diesel engine 1 to the outside, and the burner device 7, the agitation unit 8, and diesel are sequentially installed in the passage from the upstream side. An oxidation catalyst (DOC: Diesel Oxidation Catalyst) 9 and a diesel particulate filter (DPF: Diesel Particulate Filter) 10 are provided. The exhaust system includes a burner device 7, a stirring unit 8, a diesel oxidation catalyst 9 as an oxidation catalyst, and a diesel particulate filter 10 as a particulate filter. Hereinafter, the diesel particulate filter 10, the diesel oxidation catalyst 9, the burner device 7, and the stirring unit 8 will be described in this order.

(Diesel particulate filter 10)
As shown in the longitudinal sectional view of FIG. 1B, the diesel particulate filter 10 is composed of a porous body 10a in which ceramic or metal is formed in a honeycomb structure. The diesel particulate filter 10 collects particulate matter 20 having a size of, for example, 10 microns or more contained in the exhaust gas of the diesel engine 1 (indicated by an arrow in FIG. 1B), and extracts the particulate matter 20 from the exhaust gas. The particulate matter 20 is separated. The exhaust gas from which the particulate matter 20 is thus separated is discharged to the outside. At this time, if the particulate matter 20 is excessively deposited on the diesel particulate filter 10, the porous body 10a may be clogged. Clogging causes an increase in exhaust pressure, leading to deterioration in fuel consumption and output. Therefore, the following diesel oxidation catalyst 9 is provided.

(Diesel oxidation catalyst 9)
The diesel oxidation catalyst 9 is provided upstream of the diesel particulate filter 10 and is made of a catalyst such as platinum or palladium. Then, the oxygen contained in the exhaust gas of the diesel engine 1 is utilized to raise the temperature of the exhaust gas by catalytic combustion of unburned fuel (oxidation via the catalyst). The heated exhaust gas flows to the downstream diesel particulate filter 10, burns the particulate matter 20 deposited on the diesel particulate filter 10 and exhausts it as carbon dioxide, and eliminates the clogging of the diesel particulate filter 10. To do. Such a series of processing is referred to as filter regeneration processing in the present embodiment.

  Such a filter regeneration process is a batch process that is executed for a desired time at a desired timing until the clogging of the diesel particulate filter 10 exceeds a predetermined threshold and the clogging is eliminated to some extent. It is. However, the diesel oxidation catalyst 9 may not reach the activation temperature at which the temperature of the exhaust gas is low and oxidation is promoted when the diesel engine 1 is started or when the load is low. In the diesel particulate filter 10 located in the position, the filter regeneration process may not be performed at a desired timing. Therefore, in the present embodiment, the following burner device 7 is provided.

(Burner device 7)
FIG. 2 is an explanatory diagram for explaining the structure of the burner device 7. In the present embodiment, the X axis, the Y axis, and the Z axis that intersect perpendicularly are defined as shown in FIG. The burner device 7 raises the temperature of the gas and raises the temperature of the exhaust gas in addition to the exhaust gas discharged from the exhaust port of the diesel engine 1. In this way, the temperature increase of the diesel oxidation catalyst 9 can be assisted. That is, it is possible to perform the filter regeneration process by raising the diesel oxidation catalyst 9 to the activation temperature at a desired timing.

  The specific structure of the burner device 7 will be described. The outer wall 50 of the burner device 7 is formed in, for example, a rectangular tube shape, and the lower end in the direction along the Z axis communicates with the exhaust flow path 6. The end is occluded. A first partition member 52 that partitions the inside of the outer wall 50 in the X-axis direction is disposed inside the outer wall 50. The first partition member 52 is made of, for example, a rectangular plate, and three of the outer peripheral side surfaces are fixed to the closed surface of the outer wall 50 and the inner peripheral surface in the Y-axis direction, and the other one side surface is the exhaust flow. Projects to the road 6. The outer wall 50 and the first partition member 52 form an inflow path 54. The inflow path 54 is open to the exhaust flow path 6, and a part (for example, about 20%) of the exhaust gas flowing into the exhaust flow path 6 flows in by the first partition member 52 protruding into the exhaust flow path 6. It flows into the channel 54.

  Of the spaces partitioned by the first partition member 52 inside the outer wall 50, the space located downstream in the X-axis direction is further partitioned by the second partition member 56 in the Z-axis direction. The second partition member 56 is made of, for example, a rectangular plate material, and the outer peripheral side surface is fixed to the first partition member 52 and the inner peripheral surface of the outer wall 50. The space above the Z axis partitioned by the second partition member 56 is a primary combustion chamber 58 for generating a flame, and the space below the Z axis is a secondary combustion chamber 60 for promoting combustion.

  The gas supply unit 62 is configured by, for example, an air pump, and supplies a gas other than the exhaust gas, that is, air in the present embodiment, to the primary combustion chamber 58, and assists the generation of a flame in the primary combustion chamber 58. The gas supply unit 62 is not limited to an air pump, and may be configured with a fan, a compressor, or the like. Here, the first partition member 52 is provided with a hole 52 a penetrating from the inflow path 54 to the primary combustion chamber 58, and air is guided to the primary combustion chamber 58 through the hole 52 a. The hole 52a also serves to limit the air flow rate.

  However, if only air is introduced into the primary combustion chamber 58, the temperature of the air must be raised to some extent, and the absolute amount of air required to generate a flame increases. Therefore, in the present embodiment, as described above, a part of the exhaust gas is caused to flow from the exhaust passage 6 to the inflow passage 54 to generate an air-fuel mixture (hereinafter simply referred to as an air mixture). Then, the air mixture is introduced into the primary combustion chamber 58.

  FIG. 3 is an explanatory diagram comparing the required amount of air when the diesel engine 1 is idling. As can be understood with reference to FIG. 3, when the exhaust gas is mixed with the air, the required amount of air can be reduced at each engine speed as compared with the case where only the air is introduced without using the exhaust gas.

  Returning to FIG. 2, the first partition member 52 is provided with a hole 52 b penetrating from the inflow path 54 to the secondary combustion chamber 60, and the exhaust gas is guided to the secondary combustion chamber 60 by the hole 52 b. The holes 52b also serve to limit the flow rate of the exhaust gas that is led to the secondary combustion chamber 60.

  Further, the second partition member 56 is provided with a hole 56a penetrating from the primary combustion chamber 58 to the secondary combustion chamber 60, and the air mixture burned in the primary combustion chamber 58 by the hole 56a is subjected to secondary combustion. Guided to chamber 60. The hole 56a also serves to limit the flow rate of the air-fuel mixture. Thus, the flow rate of the air-fuel mixture in the primary combustion chamber 58 and the secondary combustion chamber 60 is suppressed, so that the ignitability and flame holding performance are improved in the primary combustion chamber 58, and the flame in the secondary combustion chamber 60 is improved. The temperature range and oxygen concentration range where combustion can be started can be expanded.

  The primary fuel supply unit 70 (fuel supply unit) is constituted by a fuel injection device such as an injector having a nozzle, for example, and supplies the fuel to the primary combustion chamber 58 in the form of a mist. The ignition unit 72 is configured by an ignition device such as a glow plug, for example, and is heated to a temperature equal to or higher than the fuel ignition temperature to ignite the fuel and air mixture vaporized by the heat of the ignition unit 72.

  The fuel holding part 72a is disposed in the vicinity of the ignition part 72, for example, at a position covering one end of the ignition part 72, and is, for example, porous such as a wire mesh, sintered metal, metal fiber, glass cloth, ceramic porous body, ceramic fiber, pumice, etc. The air mixture is led from the hole 52a, and the fuel is temporarily held until the fuel supplied from the primary fuel supply unit 70 is combusted. Here, the fuel holding portion 72a may be a catalyst formed as a porous body.

  The baffle plate 74 is formed of, for example, a rectangular plate material, and one end is fixed to the closing surface of the outer wall 50 and the other end side is disposed at a position facing the hole 52a. The baffle plate 74 prevents the air mixture flowing into the primary combustion chamber 58 through the holes 52 a from directly colliding with the ignition unit 72. With this configuration, the flow velocity of the air-fuel mixture in the vicinity of the ignition unit 72 can be suppressed, and the ignitability is improved.

  Similar to the primary fuel supply unit 70, the secondary fuel supply unit 76 is configured by a fuel injection device such as an injector and supplies the fuel into the secondary combustion chamber 60 in the form of a mist. In the secondary combustion chamber 60, in order to amplify the seed fire generated in the primary combustion chamber 58, fuel is further injected by the secondary fuel supply unit 76, and combustion of the air-fuel mixture is promoted while entraining exhaust gas.

  Then, the high-temperature air mixture after the temperature rises flows into the exhaust passage 6 and mixes with the exhaust gas that has not flowed into the burner device 7 to increase the temperature of the exhaust gas. In this way, the diesel oxidation catalyst 9 is heated to the activation temperature, and the filter regeneration process can be performed in the diesel particulate filter 10.

  However, in the present embodiment, since the burner device 7 stands vertically with respect to the exhaust passage 6, the heated gas is outside the flow of the exhaust gas in the exhaust passage 6. From one direction (Z direction in FIG. 2). Therefore, the temperature distribution is uneven and non-uniform in the cross section of the exhaust flow path 6. Therefore, in the present embodiment, the following stirring unit 8 is provided.

(Stirring unit 8)
FIG. 4 is a cross-sectional view for explaining the structure of the stirring unit 8. The stirring unit 8 is formed as a part of the exhaust passage 6 downstream of the burner device 7 and upstream of the diesel oxidation catalyst 9, and expands the cross-sectional area of the exhaust passage 6 along the flow of the exhaust gas. Then, the flow path cross-sectional area is reduced. In other words, the cross-sectional area of the flow path in the stirring unit 8 is larger than the cross-sectional area of the exhaust flow path 6 immediately before and the cross-sectional area of the exhaust flow path 6 immediately after that. Here, it is assumed the cylindrical tube as the exhaust passage 6, the diameter d ₁ of the agitating portion 8 than the diameter d ₃ of the exhaust passage 6 immediately after the diameter d ₂ and the exhaust passage 6 immediately before growing.

  The mixed gas of the exhaust gas not passing through the burner device 7 and the gas heated by the burner device 7 (hereinafter simply referred to as the exhaust gas mixture) indicated by the arrow in FIG. At the position 8a where the road cross-sectional area expands, the speed is rapidly decelerated and the direction of the flow path becomes uneven. Thus, the exhaust gas mixture is stirred and uniformed in the inside 8b of the stirring unit 8. Further, the exhaust gas mixture rapidly increases at a position 8c where the flow path cross-sectional area of the agitating unit 8 is reduced, and the cross-sectional area of the flow path is narrowed, so that the exhaust gas mixture is made more uniform.

  Such a stirring unit 8 has a small pressure loss and a simple configuration as compared with a swirler, a baffle plate, and the like, and therefore can suppress the manufacturing cost. Therefore, it is possible to enhance the mixing effect and easily make the temperature distribution uniform with a simple and low-cost configuration with low pressure loss.

  FIG. 5 is a cross-sectional view for explaining another structure of the stirring unit. Here, the side surface 18a of the stirring unit 18 is curved, and as shown by arrows in FIG. 5, the inflow direction of the exhaust gas mixture flowing into the stirring unit 18 and the outflow direction of the exhaust gas mixture flowing out of the stirring unit 18 (The inflow direction and the outflow direction are not on a straight line or are not parallel).

  Here, the exhaust gas mixture decelerated at the position 18b where the flow path cross-sectional area of the agitation unit 18 expands collides with the curved side surface 18a and is agitated to promote uniform temperature distribution.

  FIG. 6 is a cross-sectional view for explaining still another structure of the stirring unit. Here, for example, the agitating portion 28 is formed in a rectangular parallelepiped whose entire surface is larger in area than the flow passage cross section of the exhaust flow path 6, and the exhaust gas mixture flows in from any surface and is in a positional relationship perpendicular to the surface. Let the exhaust gas mixture flow out of the surface.

  Therefore, as indicated by arrows in FIG. 6, the inflow direction of the exhaust gas mixture flowing into the stirring unit 28 and the outflow direction of the exhaust gas mixture flowing out of the stirring unit 28 are in a vertical positional relationship. The exhaust gas mixture decelerated at the position 28a where the road cross-sectional area expands collides with the opposed surface 28b and is agitated to promote uniform temperature distribution.

  As described above, according to the exhaust system of the present embodiment, the mixing effect can be enhanced and the temperature distribution can be easily uniformed with the simple configuration of the stirring unit 8 that has a small pressure loss and can suppress the cost. It becomes.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this embodiment. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Is done.

  For example, in the above-described embodiment, the configuration in which a part of the exhaust gas is heated together with air and reduced to the burner device has been described as the burner device. However, the configuration in which the exhaust gas is directly combusted in the exhaust passage 6, etc. Various temperature rising modes can be employed.

  INDUSTRIAL APPLICABILITY The present invention can be used in an exhaust system that mixes an exhaust gas flowing through an exhaust passage with a gas heated by a burner device and assists oxidation of an oxidation catalyst.

1 ... Diesel engine (engine)
6 ... Exhaust flow path 7 ... Burner device 8, 18, 28 ... Stirrer 9 ... Diesel oxidation catalyst (oxidation catalyst)
10 ... Diesel particulate filter (particulate filter)
20 ... Particulate matter

Claims (1)

A particulate filter that collects particulate matter contained in the exhaust gas discharged from the engine;
An oxidation catalyst that is provided upstream of the particulate filter and raises the temperature of the exhaust gas by an oxidation reaction via the catalyst;
Provided upstream of the oxidation catalyst, a part of the exhaust gas is allowed to flow into the exhaust gas so that the oxidation catalyst has an oxidation activation temperature, and the exhaust gas is perpendicular to the flow of the exhaust gas. A burner device to be introduced into,
An agitator formed in a rectangular parallelepiped shape provided downstream of the burner device and upstream of the oxidation catalyst, the flow passage cross-sectional area being enlarged along the flow of the exhaust gas, and then the flow passage cross-sectional area being reduced; ,
With
Causing the exhaust gas to flow out from a surface perpendicular to the surface into which the exhaust gas flows in the stirring portion formed of the rectangular parallelepiped,
The exhaust system according to claim 1, wherein an outflow direction of the exhaust gas flowing out from the stirring unit is perpendicular to an inflow direction of the exhaust gas flowing into the stirring unit.

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